Nahanni National Park Reserve, National park reserve in Dehcho Region, Northwest Territories, Canada

Nahanni National Park Reserve is a protected area in the southwestern Northwest Territories, built around the South Nahanni River and its tributaries. The landscape includes deep canyons with rock walls, hot springs, waterfalls, and valleys shaped by glaciers.

Nahanni National Park Reserve was established in 1972 by Prime Minister Pierre Trudeau, initially covering 4,766 square kilometres. In 1978 it was among the first four natural sites inscribed on the UNESCO World Heritage List. A 2003 agreement with the Dehcho Dene gave interim protection to 23,000 square kilometres, and in 2007 Prime Minister Stephen Harper added 5,400 square kilometres, bringing the park to 33,000 square kilometres, Canada's third largest.

The name derives from the Dene term Nahʔa Dehé, "river of the land of the Nahʔa people". The Dene know Virginia Falls as Nailicho, and the park's canyons were named by prospectors who numbered them while travelling upriver. A 2003 agreement between Northwest Territories Dene and the Canadian government gave provisional protection to 23,000 km².

Travelers reach the reserve by charter plane or boat, as no roads lead into the remote wilderness. Reservations must be made months ahead, especially for summer months when conditions favor paddling and hiking.

The falls were once farther downstream at the east end of Fourth Canyon; their retreat upstream through the limestone carved that canyon and left Mason's Rock, a resistant spire in the centre of the falls named after canoeist and filmmaker Bill Mason (1929–1988).